I'm on a lot of different Harley forums. When this has happened, one common factor I've noticed, is I bet 80% of the people who have experienced this issue, are heel shifters.

 

A common problem. Apparently the MOCO isn't capable of designing a unit that simply works and stays on the bike.

Nothing new here.

 

So what's a good solution?
I'm reading put blue or red locktite on what - the splines? the screw threads?
I was thinking since there is a groove on the shaft perpendicular to the splines, why not drill/tap a 1/4" hole to line up with that groove and put a set screw into it. Locktite THAT screw into place and regardless of the OE clamping screw loosening, the set screw in the groove should prevent it from sliding off.
My own story, bought a used 14 Ultra Limited. Found a 2 YO service tag saying the shifter had fallen off. Two days later, I went to heel shift - and it was gone. So now back to get a 3rd one for this bike.
One other thing to mention, if you have not pulled your shift shaft out and lubed it - do it soon before it has so much vibration you wont believe. I have 100K+ on my 05 and finally had to have the bushing replaced. I also put in a Pingle greasable shaft so I can lube it once a year. The steel shaft wears on the brass bushing through the inner primary housing. I'll probably be putting a Pingle in this '14 next year.